1. Field of the Invention
The present invention relates to a speed reducing mechanism, and in particular to a zero backlash planetary gear train capable of eliminating backlash.
2. The Prior Arts
In general, the planetary gear train is used to reduce rotation speed and raise output torsion, and it can have various types and structures. Due to imperfections of manufacturing precision, so that during assembly, very large or small backlash may occur, and that is rather difficult to correct, thus severely affecting precision in forward and reverse rotations, and its overall performance.
In this respect, refer to Taiwan Patent No. 201022563A1, wherein, relative displacement between slant gear pairs are adjusted to reduce gear backlash between sun gear and planetary gear, and the planetary gear and the internal gear. As shown in FIG. 1, the housing 50 is provided with a straight tooth section 52, and a planetary gear set 54. The planetary gear set 54 is provided with a plurality of planetary gears 56, each of which is engaged respectively with the straight tooth section 52 and the sun gear slant tooth section 58 of input axis. In such a structure, through adjusting the relative positions of the sun gear slant tooth sections 58 and the planetary gear, the function of adjusting backlash can be achieved. However, due to different degrees of precision for the various gears, the backlashes between sun gear 60 and various planetary gears 56 can not be reduced to zero at the same time. Also, along with increase of usage, the wear of tooth faces tends to increase backlashes between gear pairs, and presently that can only be adjusted manually, and can not be achieved automatically.
Also, refer to U.S. Patent No. 20040089089. Wherein, as shown in FIG. 2, the gear train is composed of a first gear 62, a second gear 64, and a third gear 66. An elastic body 68 is disposed between the respective gears to make the gears to produce relative rotations, so as to eliminate automatically backlash between the upper and lower gear pair engaged to each other. The shortcomings of this structure are that, since the elastic body 68 is deformed under force, so that a slight time difference exists between outputs of torques. Also, the stiffness of the overall structure is insufficient for use in large horse power transmission mechanism. Moreover, in this kind of design, during assembly, additional fixtures are required.
From the descriptions mentioned above, it can be known that, presently, the backlash regulating and eliminating mechanism of the planetary gear is not able to provide the various advantages required for the gear pairs at the same time: automatic backlash elimination, zero time difference of torque transmission, high stiffness, easy assembly, and suitable to use in various planetary gear structures.
Therefore, presently, the design and performance of gear backlash eliminating mechanism is not quite satisfactory, and it has much room for improvements.